1. Field of the Invention
The present invention relates to a method for preparing 4-aminodiphenylamine (hereunder referred to as “4-ADPA”) from carbanilide (diphenylurea) and nitrobenzene. More particularly, it relates to a method for preparing 4-ADPA by the reaction of carbanilide and nitrobenzene, in the presence of an appropriate organic base or a mixture of an organic base and an inorganic base, to prepare 4-nitrodiphenylamine (hereunder referred to as “4-NDPA”) and 4-nitrosodiphenylamine (hereunder referred to as “4-NODPA”) with good selectivity and yield and continuously reducing these 4-nitro- or 4-nitroso-diphenylamine intermediates with an appropriate catalyst and hydrogen without a separation process, i.e., without separating the 4-NDPA and 4-NODPA intermediates.
2. Description of the Related Art
In general, 4-ADPA is widely used to prepare (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine) (“6PPD”), (N-isopropyl-N-phenyl-p-phenylenediamine) (“IPPD”), etc., by reductive alkylation, which may be utilized as anti-aging agents of rubbers.
The known industrial preparation processes of 4-ADPA can be classified into three groups. They are the Monsanto process, the Ouchi process and the NASH (nucleophilic aromatic substitution for hydrogen) process.
In the Monsanto process, chlorobenzene is nitrated to p-chloronitrobenzene, and then reacted with formanilide to prepare 4-NDPA. Then, 4-NDPA is hydrogenated to prepare 4-ADPA. In this preparation method, treatment of corrosive wastewater containing chlorine and a large amount of organic and inorganic waste liquids are required.
In the Ouchi process, diphenylamine is reacted with sodium nitrite (NaNO2) to prepare N-nitrosodiphenylamine, which undergoes Fischer-Hepp rearrangement, neutralized and then hydrogenated to prepare 4-ADPA. This process has the problem of generation of a large volume of harmful waste liquid during the nitrosation process.
The third process, or NASH process, has been proposed as an alternative to the above processes generating harmful materials.
One NASH process involves directly reacting aniline and nitrobenzene in the presence of base, such as, tetramethylammonium hydroxide (hereunder referred to as “TMAH”) to prepare 4-NDPA and 4-NODPA (J. Am. Chem. Soc., 1992, 114(23), 9237–8; U.S. Pat. No. 5,117,063; U.S. Pat. No. 5,252,737; U.S. Pat. No. 5,331,099; U.S. Pat. No. 5,453,541; U.S. Pat. No. 5,552,531; U.S. Pat. No. 5,633,407). This process is able to reduce the amount of waste and environmentally harmful materials.
However, this method is disadvantageous in that excessive byproducts, such as, 2-nitrodiphenylamine (hereunder referred to as “2-NDPA”), phenazine and azobenzene, are generated because aniline tends to react at the ortho site of nitrobenzene.
Other proposed methods of preparing 4-ADPA include head-to-tail addition of aniline (U.S. Pat. No. 4,760,186) and hydrogenation of p-nitrosodiphenylhydroxylamine. However, these methods are disadvantageous in production efficiency and in economic aspect. As a new preparing method using the NASH reaction process to prepare 4-ADPA, reaction of aniline and azobenzene in the presence of base such as TMAH (J. Org. Chem., 1994, 59(19), 5627–5632; U.S. Pat. Nos. 5,382,691 and 5,618,979, EP No. 726,889, WO No. 95/12569, JP No. 9504546) is also known. But, this method is also disadvantageous in production yield.
Another method of using the NASH reaction with an anilide as starting material, involves reacting acetanilide and nitrobenzene in a DMSO solvent in the presence of NaOH and K2CO3 to prepare 4-NODPA (Tetrahedron Letters, vol. 31, No. 22, pp 3217–3210, 1990). However, the acetanilide is unstable under the reaction conditions and by-products are generated by the decomposition of starting materials.
More recently, the NASH reaction has been used to react carbanilide and nitrobenzene in a dimethylsulfoxide (hereunder referred to as “DMSO”) solvent in the presence of NaOH, an inorganic base, to prepare 4-NDPA (U.S. Pat. No. 5,684,203, WO No. 0051966). This method requires recycling of the inorganic base and use of the expensive DMSO solvent. Also, removal of DMSO solvent is required prior to hydrogenation to avoid possible poisoning of precious metal catalyst.